Partially oxidized sulfur oxyanions, such as, thiosulfate (S.sub.2 O.sub.3.sup.2-), tetrathionate (S.sub.4 O.sub.6.sup.2-) and trithionate (S.sub.3 O.sub.6.sup.2-), which are collectively known as thiosalts, are formed during the milling and flotation processing of sulfide ores. These residual constituents in mill tailings waters are converted into sulphuric acid by bacterial action at a sufficiently rapid rate as to result in an environmental problem when the tailings are discharged into river systems.
Complete oxidation of the thiosalts to sulfuric acid by chemical or biochemical means and neutralization of the acid by lime prior to discharge of the effluent to receiving streams has long been considered a viable solution to the problem, provided that a simple and economic means of oxidation of thiosalts in large volumes of water can be developed. To this end, the possibility of using catalyzed oxidation of the thiosalts by air to sulfate has been the subject of active research, ever since the finding that suitably complexed copper (II) ions homogeneously catalyze the oxidation of thiosulfate to sulfate by molecular oxygen, as described by Byerley et al in J. Chem. Soc., Dalton Trans. 1975, 1329. Research efforts were directed at developing polymer-supported catalysts having this property, since the provision of a supported catalyst would facilitate economic recovery and reuse of the catalyst and, in this way, provide a potentially low cost method for the removal of thiosalts.
Following the preparation and testing of a number of polychelates for their catalytic activity, poly(4-vinyl pyridine)-Cu(II) complexes were developed as effective catalysts, as described by Chanda et al. in J. Molecular Catal. 1980, 7, 389 and in J. Molecular Catal. 1981, 11, 9. Subsequent attempts to improve the activity and stability of these PVP-CU(II) catalysts succeeded in developing a PVP-CU(II) complex of optimum composition based on a quantitative understanding of the relation between catalytic activity and distribution of different coordinate species of the polychelate (See Chanda et al. J. Molecular Catal. 1980, 61, 533). Further enhancement of activity and stability of the complex were achieved by cross-linking quaternization of the residual free pyridine units in the complex of optimum composition (Chanda et al., J. Molecular Catal. 1981, 12, 197).
Although the polymer-supported Cu(II) catalysts exhibited high activity and stability during batch oxidation runs lasting a few hours, continuous oxidation runs conducted over several weeks using slurry reactors and air as both the source of oxygen and agitation means for the slurry, resulted in a slow deactivation of the catalyst with time due to leakage of copper ions and slow degradation of the polymer base (Chanda et al., Final Report (Oct. 1980) on Energy, Mines and Resources Canada Research Agreements Program Nos. 274-2-78, 56-2-79 and 54-2-80).